The present invention relates to an enclosure for an electrical motor of the explosion proof type, and which incorporates a novel opening structure for the electrical cable.
Electrically operated equipment which is intended for use in coal mines must conform to the strict construction and design requirements of 30 CFR 18.20 et seq to insure safety for its intended use. Among the requirements are those intended to render electrical motors explosion proof in a mine environment, and included in this category are detailed specifications for the openings in the motor enclosure that are provided for the electrical cable entrances. For example, such openings must be of at least a specified length and diameter, and the walls of the openings must be of a specified surface finish.
Presently, the electrical cable openings in motor enclosures include a tubular metal adapter which is threadedly received in the opening of the enclosure, and a tubular cylindrical plug which is coaxially received within the adapter. The cylindrical plug includes an end portion which extends outwardly beyond the wall of the enclosure, and a circumferential groove is positioned in the end portion of the plug. A clamp plate is then positioned so as to be received in the circumferential groove of the plug, and the clamp plate is in turn secured to the outer surface of the adapter by a threaded bolt.
In order to prevent the unintended unthreading and removal of the adapter from the opening, along with the plug and the attached clamp plate, it has been necessary to secure the adapter to the wall of the enclosure by means of external devices, such as bolts, cables, or welding. These external devices cause difficulty in the event the opening or electrical cable is damaged through the rough usage often encountered in mines, and when repair is required. In such cases, it is necessary to first remove the external attachment devices, i.e. the bolts, cables, or welding, which secure the adapter to the wall of the enclosure, and it is then necessary to reattach these devices when the repair is completed. The environment within a mine for conducting these repairs is often confining and dirty, rendering the repair operation tedious and difficult.
Some of the commonly employed attachment devices, such as bolts which are threaded into openings in the enclosure wall, require that the adapter be precisely bottomed to insure that the bolts properly engage the adapter. Such precise buttoning also can be difficult to verify in the field.
It is accordingly an object of the present invention to provide an enclosure for an electrical motor of the explosion proof type which includes electrical cable openings which significantly alleviate the difficulty of making repairs in the field.